Various types of supervisory apparatus for the operation of bearings have been proposed. Generally, the relative movement between the rotor or rotating part of the bearing with respect to the stator can be checked electronically by using inductive or capacitative transducers to avoid the necessity of contacting elements. Other transducers use eddy current effects. Such apparatus are complex and require application of components to the stationary as well as to rotating portion of the bearing, for example insulated electrodes, electronic transducers and pick-ups, or the like. The presence of lubricant, typically oil, which may be contaminated with dirt or other particles and especially with metal particles derived from the machine portions themselves may interfere with providing an output which is accurately representative of the operation of the bearing as such. The insulating qualities of lubricating oil, for example, can be changed rapidly by the presence of chips, metal dust, or the like, which can be contained therein. Thus, the outputs from such transducer elements are not necessarily truly representative of the condition of the bearing, or the operating condition of the rotating portion thereof.
Temperature of operation is another factor which has to be considered in the selection of a suitable supervisory transducer; many transducer elements cannot operate at high temperatures and, generally, the temperature at which the bearing operates should not be in excess of 80.degree. C. Exhaust gas turbines in which an internal bearing is used may reach bearing temperatures in the order of 200.degree. C. and more when the prime moving motor, from which the exhaust gases are derived, is stopped.
It has also been proposed to supervise the uniformity of rotation by utilizing sensors which respond to vibration or other momentary deflections, similarly to seismic transducers located at the housing of the bearing or some other stationary portion of the structure with which the bearing is associated, for example on a stationary portion of the exhaust gas turbine. It is difficult to obtain accurate output signals truly representative of the operation of the bearing since the output signals are distorted due to the shape and structure of various housing portions which can be triggered to inherent oscillations or vibrations with respectively associated critical frequencies which may occur during rotation of the exhaust gas turbine rotor.